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    SubjectRe: [PATCH v3 5/6] ARM: pinctrl: Add Broadcom Capri pinctrl driver
    On 13-12-18 03:56 PM, Sherman Yin wrote:
    > On 13-12-12 12:54 PM, Linus Walleij wrote:

    >>> +/*
    >>> + * Write to the register using the value and mask if current value
    >>> is different
    >>> + */
    >>> +static void capri_reg_write(struct pinctrl_dev *pctldev,
    >>> + void __iomem *reg,
    >>> + u32 val,
    >>> + u32 mask)
    >>> +{
    >>> + u32 old_val;
    >>> + u32 new_val;
    >>> +
    >>> + old_val = readl(reg);
    >>> + new_val = (old_val & ~mask) | (val & mask);
    >>> +
    >>> + if (new_val == old_val) {
    >>> + dev_dbg(pctldev->dev,
    >>> + "Reg 0x%p=0x%x (no change)\n",
    >>> + reg, old_val);
    >>> + return;
    >>> + }
    >>> +
    >>> + dev_dbg(pctldev->dev,
    >>> + "Reg 0x%p change from 0x%x to 0x%x\n",
    >>> + reg, old_val, new_val);
    >>> + writel(new_val, reg);
    >>> +}
    >>
    >> This is a reimplementation of regmap for MMIO.
    >> See drivers/base/regmap/regmap-mmio.c
    >> Notice how regmap_update_bits() is used throughout the
    >> kernel.
    >>
    >> If you want to do this, use regmap.
    >
    > Ok.

    As you can see in v4 of my patchset, I've changed my driver to use the
    mmio regmap. However, as I was tracing through regmap_update_bits(), it
    looks like I have to go through a lot of checks and function pointers
    just to do a simple write to a register. Also, I have to select
    REGMAP_MMIO which brings in a bunch of code as well.

    I understand the benefits of using common code, but in this case it
    seems there is a lot of extra code and run-time overhead to use regmap.
    In the end it also doesn't buy much in terms of functionality.

    Just a quick note - it looks like the 2nd parameter of
    regmap_update_bits() wants the offset of a register (offset from
    regmap_mmio_context.regs). So calling the parameter "reg" is a little
    confusing, at least in the MMIO case.

    Regards,
    Sherman


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